1. Field of the Invention
This invention relates to pneumatic tires and more particularly to a novel bead construction for heavy duty pneumatic tires.
2. Prior Art
Generally, heavy duty or high load bearing pneumatic tires include a radial carcass having at least one ply of rubberized steel cord fabric wrapped about a pair of bead cores formed from tightly packed windings of wires to create carcass flippers or turnups. Bead reinforcement strips may be arranged in a folding zone and extend radially outwardly beyond the turnups, and are usually separated therefrom by rubber masses. Positioned above each bead core and extending radially outwardly therefrom between the turnups if provided and the carcass ply is an apex strip of a hard rubber compound.
The purposes of the bead core are to guarantee a reliable seating of the tire on a wheel rim and to transmit to the rims the forces generated in the steel cords of the carcass due to the inflation pressure of the tire as well as operational loads. These forces are transferred to the individual windings in the bead cores. It has been found that the bead core will function optimumly when all of the wires in the core are uniformly subjected to such loads.
It is known in the art to design the bead core with a rectangular cross-sectional or hexagonal cross-sectional configuration. Such bead core designs are capable of attenuating a large portion of the energy of deformation and reliably transfering to the rim the stresses resulting from the forces in the carcass. These designs however do not guarantee that the bead wires will be subjected to such stresses.
The rims on which tubeless truck tires are mounted may have steep shoulders, i.e., the seat areas are oriented at an angle of 15.degree. with respect to the tire axis. The bead cores are designed with various polygonal cross-sectional configurations such as parallelograms, trapezoids or longitudinally extending hexagons which are oriented obliquely at the same angle to the tire axis that the seat of the steep-shoulder rim is oriented. For example, in U.S. Pat. No. 3,757,844 the bead core is oriented parallel to the shoulder to guarantee that the individual windings of the core bear against the seat with equal pressure.
With conventional tapered rims, which can also be used for high load-bearing capacity tires, the seat of the rim is oriented with respect to the wheel axle at a slope of about 5.degree.. The tires mounted on such tapered rims have as a rule multi-cornered bead cores whose wire windings are oriented parallel to the wheel axle. Such a construction does not guarantee a uniform distribution of the force in the wire windings, particularly the radially inwardmost wires of the bead core.
It is toward elimination of these and other drawbacks that the present invention is directed.